Google's Clever Trick To Protect Your Photos From Theft

Unauthorised use of photos is frustrating for amateurs and often costly for professionals. Now five researchers at Google have published a paper detailing how one of the most popular methods of protecting your content, the visible watermark, can be easily and automatically circumvented by simple algorithms.

Thankfully, the team also describes how to defeat their own algorithms by designing more secure watermarks which are much more difficult to remove. A tactic which has recently been employed by stock photography site, Shutterstock, to protect its images.

Even if you’ve never used one, you’re bound to have seen visible watermarks at some point in the form of the deliberate overlaying of another image, usually a logo, on top of the original photo. This serves two functions: to make known the owner of the image and to render it unusable without first purchasing a non-watermarked original.

Watermarks, however, aren’t that tricky to remove. For example, when placed near the edge of an image, they can be simply cropped out. However, even more extreme versions, such as those plastered across an entire image, can remain vulnerable to removal through digital processing techniques.

The vulnerability occurs when several different images are protected by an identical watermark, such as might occur on a stock photography site. By comparing these watermarked images, the Google team was able to infer the full watermark pattern and then use it to reverse the watermarking process, creating accurate copies of the original pictures.

The results are much more convincing than current techniques, such as ‘painting in’ the watermark with a clone brush and leave stock photo sites, which trade in high volumes of images with similar watermarks, vulnerable to wide-scale theft.

Google's technique can automatically remove even colored watermarks such as these.

Google

This automated process works even when the watermark logo appears at different sizes and in different positions on the image. Changing the color or opacity doesn’t help either.

So how can you make your watermarks secure? The best method, according to the team, involves making small, even barely perceptible, changes to the shape of the watermark as applied to each image. These small changes in geometry proved far more effective in foiling the watermark removal process than any other because visual traces of the watermark always remained after processing.

Unfortunately, the Google team didn’t offer an automated process for generating these secure, ‘warped’ watermarks. Shutterstock has already implemented its watermark-morphing system in response to Google’s findings, but I don’t think it will be long before someone creates such a more widely available tool, especially given the large number of images now known to be vulnerable.